Energy positive domestic wastewater treatment: the roles of anaerobic and phototrophic technologies

Abstract

The negative energy balance of wastewater treatment could be reversed if anaerobic technologies were implemented for organic carbon oxidation and phototrophic technologies were utilized for nutrient recovery. To characterize the potential for energy positive wastewater treatment by anaerobic and phototrophic biotechnologies we performed a comprehensive literature review and analysis, focusing on energy production (as kJ per capita per day and as kJ m(-3) of wastewater treated), energy consumption, and treatment efficacy. Anaerobic technologies included in this review were the anaerobic baffled reactor (ABR), anaerobic membrane bioreactor (AnMBR), anaerobic fluidized bed reactor (AFB), upflow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (ASBR), microbial electrolysis cell (MEC), and microbial fuel cell (MFC). Phototrophic technologies included were the high rate algal pond (HRAP), photobioreactor (PBR), stirred tank reactor, waste stabilization pond (WSP), and algal turf scrubber (ATS). Average energy recovery efficiencies for anaerobic technologies ranged from 1.6% (MFC) to 47.5% (ABR). When including typical percent chemical oxygen demand (COD) removals by each technology, this range would equate to roughly 40-1200 kJ per capita per day or 110-3300 kJ m(-3) of treated wastewater. The average bioenergy feedstock production by phototrophic technologies ranged from 1200-4700 kJ per capita per day or 3400-13 000 kJ m(-3) (exceeding anaerobic technologies and, at times, the energetic content of the influent organic carbon), with usable energy production dependent upon downstream conversion to fuels. Energy consumption analysis showed that energy positive anaerobic wastewater treatment by emerging technologies would require significant reductions of parasitic losses from mechanical mixing and gas sparging. Technology targets and critical barriers for energy-producing technologies are identified, and the role of integrated anaerobic and phototrophic bioprocesses in energy positive wastewater management is discussed.

Characterization of biofoulants illustrates different membrane fouling mechanisms for aerobic and anaerobic membrane bioreactors

“…Unlike the AeMBR, which has already found widespread application in low to medium strength municipal wastewater treatment [3], AnMBRs have been considered impractical for similar applications due to the perception that comparable transmembrane flux rates are not achievable. Nonetheless, the AnMBR has continued to gain consideration as an alternative treatment technology for municipal wastewater due to its potential advantages in reduced energy input, energy generation by methane production, and low sludge production [4][5][6][7].…”

Estimating the Energy Content of Wastewater Using Combustion Calorimetry and Different Drying Processes

“…Assuming that this energy could be technically exploited, the current energy sink of wastewater treatment can be transformed into a resource with an energy balanced water resource recovery facility being a grand step ahead. Besides physical processes for wastewater valorization, e.g., by exploiting its thermal energy content (Meggers and Leibundgut, 2011) and nutrient recovery (e.g., nitrogen, phosphorus), technologies based on anaerobic and phototropic metabolisms are under examination (McCarty et al, 2011;Shoener et al, 2014).…”

Design of anaerobic membrane bioreactors for the valorization of dilute organic carbon waste streams

“…17 If unutilized, dissolved methane would ultimately be lost to the atmosphere as a fugitive emission (i.e., an unintended release to the natural environment), reducing bioenergy production and undermining broader goals to reduce global warming potential (GWP; methane is approximately 28 times worse than CO 2 on a 100 year time horizon 68 ). In order to recover all produced methane, the potential use of a degassing membrane (DM) was also included to quantify the trade-offs (in terms of cost and environmental impacts) of recovering methane or releasing it to the atmosphere.…”

“…Beyond methane, nutrient management is a critical challenge for many utilities, creating opportunities for downstream nitrogen removal 26,62 or the development of more comprehensive resource recovery strategies through the integration of phototrophic bioprocesses (e.g., microalgae cultivation for energy positive nutrient recovery). 17 …”